Physics of Semiconductor Devices Third Edition

S. M. Sze Department of Electronics Engineering National Chiao Tung University Hsinchu, Taiwan

and

Kwok K. Ng

Central Laboratory MVC (a subsidiary of ProMOS Technologies,Taiwan) San Jose, California

@ZZClE*CE A JOHN WILEY & SONS, JNC., PUBLICATION

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Physics of Semiconductor Devices

This Page Intentionally Left Blank

Physics of Semiconductor Devices Third Edition

S. M. Sze Department of Electronics Engineering National Chiao Tung University Hsinchu, Taiwan

and

Kwok K. Ng

Central Laboratory MVC (a subsidiary of ProMOS Technologies,Taiwan) San Jose, California

@ZZClE*CE A JOHN WILEY & SONS, JNC., PUBLICATION

Description of cover photograph.

A scanning electron micrograph of an array of the floating-gate nonvolatile semiconductor memory (NVSM) magnified 100,000times. NVSM was invented at Bell Telephone Laboratories in 1967. There are more NVSM cells produced annually in the world than any other semiconductor device and, for that matter, any other human-made item. For a discussion of this device, see Chapter 6. Photo courtesy of Macronix International Company, Hsinchu, Taiwan, ROC.

Copyright 0 2007 by John Wiley & Sons, Inc. All rights reserved Published by John Wiley & Sons, Inc., Hoboken, New Jersey. Published simultaneously in Canada. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4470, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 11 1 River Street, Hoboken, NJ 07030, (201) 748-601 I , fax (201) 748-6008, or online at http://www.wiley.com/go/permission. Limit of LiabilityiDisclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.

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Preface Since the mid-20th Century the electronics industry has enjoyed phenomenal growth and is now the largest industry in the world. The foundation of the electronics industry is the semiconductor device. To meet the tremendous demand of this industry, the semiconductor-device field has also grown rapidly. Coincident with this growth, the semiconductor-device literature has expanded and diversified. For access to this massive amount of information, there is a need for a book giving a comprehensive introductory account of device physics and operational principles. With the intention of meeting such a need, the First Edition and the Second Edition of Physics of Semiconductor Devices were published in 1969 and 1981, respectively. It is perhaps somewhat surprising that the book has so long held its place as one of the main textbooks for advanced undergraduate and graduate students in applied physics, electrical and electronics engineering, and materials science. Because the book includes much useful information on material parameters and device physics, it is also a major reference for engineers and scientists in semiconductor-device research and development. To date, the book is one of the most, if not the most, cited works in contemporary engineering and applied science with over 15,000 citations (ISI, Thomson Scientific). Since 1981, more than 250,000 papers on semiconductor devices have been published, with numerous breakthroughs in device concepts and performances. The book clearly needed another major revision if it were to continue to serve its purpose. In this Third Edition of Physics of Semiconductor Devices, over 50% of the material has been revised or updated, and the material has been totally reorganized. We have retained the basic physics of classic devices and added many sections that are of contemporary interest such as the three-dimensional MOSFETs, nonvolatile memory, modulation-doped field-effect transistor, single-electron transistor, resonant-tunneling diode, insulated-gate bipolar transistor, quantum cascade laser, semiconductor sensors, and so on. On the other hand, we have omitted or reduced sections of lessimportant topics to maintain the overall book length. We have added a problem set at the end of each chapter. The problem set forms an integral part of the development of the topics, and some problems can be used as worked examples in the classroom. A complete set of detailed solutions to all end-ofchapter problems has been prepared. The solution manuals are available free to all adopting faculties. The figures and tables used in the text are also available, in electronic format, to instructors from the publisher. Instructors can find out more information at the publisher’s website at http://ww.wiley.com/interscience/sze.

V

vi

PREFACE

In the course of writing this text, we had the fortune of help and support of many people. First we express our gratitude to the management of our academic and industrial institutions, the National Chiao Tung University, the National Nan0 Device Laboratories, Agere Systems, and MVC, without whose support this book could not have been written. We wish to thank the Spring Foundation of the National Chiao Tung University for the financial support. One of us (K. Ng) would like to thank J. Hwang and B. Leung for their continued encouragement and personal help. We have benefited greatly from suggestions made by our reviewers who took their time from their busy schedule. Credits are due to the following scholars: A. Alam, W. Anderson, S. Banerjee, J. Brews, H. C. Casey, Jr., P. Chow, N. de Rooij, H. Eisele, E. Kasper, S. Luryi, D. Monroe, P. Panayotatos, S. Pearton, E. F. Schubert, A. Seabaugh, M. Shur, Y. Taur, M. Teich, Y. Tsividis, R. Tung, E. Yang, and A. Zaslavsky. We also appreciate the permission granted to us from the respective journals and authors to reproduce their original figures cited in this work. It is our pleasure to acknowledge the help of many family members in preparing the manuscript in electronic format; Kyle Eng and Valerie Eng in scanning and importing text from the Second Edition, Vivian Eng in typing the equations, and Jennifer Tao in preparing the figures which have all been redrawn. We are further thankful to Norman Erdos for technical editing of the entire manuscript, and to Iris Lin and Nai-Hua Chang for preparing the problem sets and solution manual. At John Wiley and Sons, we wish to thank George Telecki who encouraged us to undertake the project. Finally, we are grateful to our wives, Therese Sze and Linda Ng, for their support and assistance during the course of the book project.

S. M. Sze Hsinchu, Taiwan Kwok K. Ng San Jose, California July 2006

Contents 1

Introduction

Part I Semiconductor Physics Chapter 1 Physics and Properties of Semiconductors-A Review 1.1 Introduction, 7 1.2 Crystal Structure, 8 1.3 Energy Bands and Energy Gap, 12 1.4 Carrier Concentration at Thermal Equilibrium, 16 1.5 Carrier-Transport Phenomena, 28 1.6 Phonon, Optical, and Thermal Properties, 50 1.7 Heterojunctions and Nanostructures, 56 1.8 Basic Equations and Examples, 62

7

Part I1 Device Building Blocks Chapter 2 p-n Junctions 2.1 Introduction, 79 2.2 Depletion Region, 80 2.3 Current-Voltage Characteristics, 90 2.4 Junction Breakdown, 102 2.5 Transient Behavior and Noise, 114 2.6 Terminal Functions, 118 2.7 Heterojunctions, 124 Chapter 3 Metal-Semiconductor Contacts 3. I Introduction, 134 3.2 Formation of Barrier, 135 3.3 Current Transport Processes, 153 3.4 Measurement of Barrier Height, 170 3.5 Device Structures, 181 3.6 Ohmic Contact, 187

79

134

Vii

viii

CONTENTS

Chapter 4 Metal-Insulator-Semiconductor Capacitors 4.1 Introduction, 197 4.2 Ideal MIS Capacitor, 198 4.3 Silicon MOS Capacitor, 213

197

Part I11 Transistors Chapter 5 Bipolar Transistors 5.1 Introduction, 243 5.2 Static Characteristics, 244 5.3 Microwave Characteristics, 262 5.4 Related Device Structures, 275 5.5 Heterojunction Bipolar Transistor, 282

243

Chapter 6 MOSFETs 6.1 Introduction, 293 6.2 Basic Device Characteristics, 297 6.3 Nonuniform Doping and Buried-Channel Device, 320 6.4 Device Scaling and Short-Channel Effects, 328 6.5 MOSFET Structures, 339 6.6 Circuit Applications, 347 6.7 Nonvolatile Memory Devices, 350 6.8 Single-Electron Transistor, 360

293

Chapter 7 JFETs, MESFETs, and MODFETs 7.1 Introduction, 374 7.2 JFET and MESFET, 375 7.3 MODFET, 401

374

Part IV Negative-Resistance and Power Devices Chapter 8 Tunnel Devices 8.1 Introduction, 417 8.2 Tunnel Diode, 418 8.3 Related Tunnel Devices, 435 8.4 Resonant-Tunneling Diode, 454

417

Chapter 9 IMPATT Diodes 9.1 Introduction, 466

466

CONTENTS

9.2 9.3 9.4 9.5 9.6 9.7 9.8

ix

Static Characteristics, 467 Dynamic Characteristics, 474 Power and Efficiency, 482 Noise Behavior, 489 Device Design and Performance, 493 BARITT Diode, 497 TUNNETT Diode, 504

Chapter 10 Transferred-Electron and Real-Space-Transfer Devices 510 10.1 Introduction, 5 10 10.2 Transferred-Electron Device, 5 11 10.3 Real-Space-Transfer Devices, 536 Chapter 11 Thyristors and Power Devices 11.1 Introduction, 548 11.2 Thyristor Characteristics, 549 11.3 Thyristor Variations, 574 11.4 Other Power Devices, 582

548

Part V Photonic Devices and Sensors Chapter 12 LEDs and Lasers 12.1 Introduction, 601 12.2 Radiative Transitions, 603 12.3 Light-Emitting Diode (LED), 608 12.4 Laser Physics, 621 12.5 Laser Operating Characteristics, 630 12.6 Specialty Lasers, 651

601

Chapter 13 Photodetectors and Solar Cells 13.1 Introduction, 663 13.2 Photoconductor, 667 13.3 Photodiodes, 671 13.4 Avalanche Photodiode, 683 13.5 Phototransistor, 694 13.6 Charge-Coupled Device (CCD), 697 13.7 Metal-Semiconductor-Metal Photodetector, 7 12 13.8 Quantum-Well Infrared Photodetector, 7 16 13.9 Solar Cell, 719

663

x

CONTENTS

Chapter 14 Sensors 14.1 Introduction, 743 14.2 Thermal Sensors, 744 14.3 Mechanical Sensors, 750 14.4 Magnetic Sensors, 758 14.5 Chemical Sensors, 765

743

Appendixes A. List of Symbols, 775 B. International System of Units, 785 C. Unit Prefixes, 786 D. Greek Alphabet, 787 E. Physical Constants, 788 F. Properties of Important Semiconductors, 789 G. Properties of Si and GaAs, 790 H. Properties of SiO, and Si,N,, 791

773

Index

793

Introduction The book is organized into five parts: Part I: Part 11: Part 111: Part IV: Part V

Semiconductor Physics Device Building Blocks Transistors Negative-Resistance and Power Devices Photonic Devices and Sensors

Part I, Chapter 1, is a summary of semiconductor properties that are used throughout the book as a basis for understanding and calculating device characteristics. Energy band, carrier concentration, and transport properties are briefly surveyed, with emphasis on the two most-important semiconductors: silicon (Si) and gallium arsenide (GaAs). A compilation of the recommended or most-accurate values for these semiconductors is given in the illustrations of Chapter 1 and in the Appendixes for convenient reference. Part 11, Chapters 2 through 4, treats the basic device building blocks from which all semiconductor devices can be constructed. Chapter 2 considers the p-n junction characteristics. Because thep-n junction is the building block of most semiconductor devices, p-n junction theory serves as the foundation of the physics of semiconductor devices. Chapter 2 also considers the heterojunction, that is a junction formed between two dissimilar semiconductors. For example, we can use gallium arsenide (GaAs) and aluminum arsenide (AlAs) to form a heterojunction. The heterojunction is a key building block for high-speed and photonic devices. Chapter 3 treats the metal-semiconductor contact, which is an intimate contact between a metal and a semiconductor. The contact can be rectifying similar to ap-n junction if the semiconductor is moderately doped and becomes ohmic if the semiconductor is very heavily doped. An ohmic contact can pass current in either direction with a negligible voltage drop and can provide the necessary connections between devices and the outside world. Chapter 4 considers the metal-insulator-semiconductor (MIS) capacitor of which the Si-based metal-oxide-semiconductor (MOS) structure is the dominant member. Knowledge of the surface physics associated with the MOS capacitor is important, not only for understanding MOS-related devices such as the MOSFET and the floating-gate nonvolatile memory but also because of its relevance to the stability and reliability of all other semiconductor devices in their surface and isolation areas. 1

2

INTRODUCTION

Part 111, Chapters 5 through 7 , deals with the transistor family. Chapter 5 treats the bipolar transistor, that is, the interaction between two closely coupled p-n junctions. The bipolar transistor is one of the most-important original semiconductor devices. The invention of the bipolar transistor in 1947 ushered in the modern electronic era. Chapter 6 considers the MOSFET (MOS field-effect transistor). The distinction between a field-effect transistor and a potential-effect transistor (such as the bipolar transistor) is that in the former, the channel is modulated by the gate through a capacitor whereas in the latter, the channel is controlled by a direct contact to the channel region. The MOSFET is the most-important device for advanced integrated circuits, and is used extensively in microprocessors and DRAMS (dynamic random access memories). Chapter 6 also treats the nonvolatile semiconductor memory which is the dominant memory for portable electronic systems such as the cellular phone, notebook computer, digital camera, audio and video players, and global positioning system (GPS). Chapter 7 considers three other field-effect transistors; the JFET (junction field-effect-transistor), MESFET (metal-semiconductor field-effect transistor), and MODFET (modulation-doped field-effect transistor). The JFET is an older member and now used mainly as power devices, whereas the MESFET and MODFET are used in high-speed, high-input-impedance amplifiers and monolithic microwave integrated circuits. Part IV, Chapters 8 through 1 1 , considers negative-resistance and power devices. In Chapter 8, we discuss the tunnel diode (a heavily dopedp-n junction) and the resonant-tunneling diode (a double-barrier structure formed by multiple heterojunctions). These devices show negative differential resistances due to quantummechanical tunneling. They can generate microwaves or serve as functional devices, that is, they can perform a given circuit function with a greatly reduced number of components. Chapter 9 discusses the transit-time devices. When a p-n junction or a metal-semiconductor junction is operated in avalanche breakdown, under proper conditions we have an IMPATT diode that can generate the highest CW (continuous wave) power output of all solid-state devices at millimeter-wave frequencies (i.e., above 30 GHz). The operational characteristics of the related BARITT and TUNNETT diodes are also presented. The transferred-electron device (TED) is considered in Chapter 10. Microwave oscillation can be generated by the mechanism of electron transfer from a high-mobility lower-energy valley in the conduction band to a low-mobility higher-energy valley (in momentum space), the transferred-electron effect. Also presented are the real-space-transfer devices which are similar to TED but the electron transfer occurs between a narrow-bandgap material to an adjacent wide-bandgap material in real space as opposed to momentum space. The thyristor, which is basically three closely coupledp-n junctions in the form of ap-n-p-n structure, is discussed in Chapter 11. Also considered are the MOS-controlled thyristor (a combination of MOSFET with a conventional thyristor) and the insulated-gate bipolar transistor (IGBT, a combination of MOSFET with a conventional bipolar transistor). These devices have a wide range of power-handling and switching capability; they can handle currents from a few milliamperes to thousands of amperes and voltages above 5000 V.

INTRODUCTION

3

Part V, Chapters 12 through 14, treats photonic devices and sensors. Photonic devices can detect, generate, and convert optical energy to electric energy, or vice versa. The semiconductor light sources-light-emitting diode (LED) and laser, are discussed in Chapter 12. The LEDs have a multitude of applications as display devices such as in electronic equipment and traffic lights, and as illuminating devices such as flashlights and automobile headlights. Semiconductor lasers are used in optical-fiber communication, video players, and high-speed laser printing. Various photodetectors with high quantum efficiency and high response speed are discussed in Chapter 13. The chapter also considers the solar cell which converts optical energy to electrical energy similar to a photodetector but with different emphasis and device configuration. As the worldwide energy demand increases and the fossil-fuel supply will be exhausted soon, there is an urgent need to develop alternative energy sources. The solar cell is considered a major candidate because it can convert sunlight directly to electricity with good conversion efficiency, can provide practically everlasting power at low operating cost, and is virtually nonpolluting. Chapter 14 considers important semiconductor sensors. A sensor is defined as a device that can detect or measure an external signal. There are basically six types of signals: electrical, optical, thermal, mechanical, magnetic, and chemical. The sensors can provide us with informations about these signals which could not otherwise be directly perceived by our senses. Based on the definition of sensors, all traditional semiconductor devices are sensors since they have inputs and outputs and both are in electrical forms. We have considered the sensors for electrical signals in Chapters 2 through 11, and the sensors for optical signals in Chapters 12 and 13. In Chapter 14, we are concerned with sensors for the remaining four types of signals, i.e., thermal, mechanical, magnetic, and chemical. We recommend that readers first study semiconductor physics (Part I) and the device building blocks (Part 11) before moving to subsequent parts of the book. Each chapter in Parts I11 through V deals with a major device or a related device family, and is more or less independent of the other chapters. So, readers can use the book as a reference and instructors can select chapters appropriate for their classes and in their order of preference. We have a vast literature on semiconductor devices. To date, more than 300,000 papers have been published in this field, and the grand total may reach one million in the next decade. In this book, each chapter is presented in a clear and coherent fashion without heavy reliance on the original literature. However, we have an extensive listing of key papers at the end of each chapter for reference and for further reading. REFERENCE 1. K. K. Ng, Complete Guide to Semiconductor Devices, 2nd Ed., Wiley, New York, 2002.